Even if genetics tell you otherwise, you can hold on to your roots a little longer with these powerful nutrients.

That said, some strands reach a point where they don't grow back. It boils down to genetics: Some guys have fewer strands growing in to replace them. By the age of 35, two-thirds of American men will experience some level of hair loss, according to the American Hair Loss Association.

Lifestyle also comes into play. Nutritional deficiencies can contribute to increased hair loss by weakening hair shafts that cause breakage and slow re-growth of new hairs.

This can potentially be reversed with the right diet. Len Glassman, a certified health nutritionist, trainer, and owner of the Personal Best Training Center, offers up the necessary nutrients that'll help keep the hairs on your head.

1. Vitamin A

An adequate intake of vitamin A is key to helping promote the growth and health of cells and tissues throughout the body, including the hair and scalp. Vitamin A gets delivered to our bodies in two ways: from plant and animal sources. Hair-healthy plant sources include red, yellow, and orange fruits, and vegetables like carrots, as well as some dark green leafy vegetables. Some heavy-hitter animal sources for vitamin A include liver, fish oil, eggs, and fortified milk.

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2. Vitamin B6, vitamin B12, and folic acid

All three of these B vitamins are essential to the normal formation of hemoglobin, which carries oxygen from the lungs to tissues in the body, including hair. Healthy, strong hair relies on a constant supply of blood and oxygen. A deficiency of these B vitamins is like cutting off the blood supply to your hair, leading to increased hair loss, damaged hair, and slow regrowth. The best sources of vitamin B6 and B12 are protein-rich foods like meat, chicken, fish, eggs, pork, and soybeans. Your best bet for plant-based sources are leafy vegetables, orange juice, avocado, beets, broccoli, wheat germ, and some fortified cereals.

3. Vitamin C

Vitamin C is essential to producing collagen, a connective tissue that gives structure by holding tissues in the body together, such as the tissue in hair. The human body is not able to store vitamin C for long periods of time, so don’t try to load up on it in an effort to make up for lost time. Instead, make sure you eat plenty of foods containing vitamin C every day. The best sources of vitamin C are found in plant sources like oranges, berries, melons, peppers, dark green leafy vegetables, and tomatoes.

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4. Zinc

Dandruff and hair loss are both conditions associated with a zinc deficiency. Zinc is a mineral that promotes cell reproduction, tissue growth, and repair. Zinc also functions in the maintenance of the oil-secreting glands attached to our hair follicles. Good sources of zinc include foods of animal origin, including seafood, poultry, mussels, shrimp, and oysters. Eggs and milk also supply zinc but in smaller amounts. Whole-grain products, nuts, seeds, and legumes contain zinc, but in a form that's not easily absorbed by the body.

5. Protein

Hair is primarily made of protein, so it makes sense to eat protein-rich foods if you’re trying to maintain healthy growth. Without adequate protein intake, the body can't efficiently make new hair to replace the hair that's shed. That said, eating a steak every day isn’t going to help you. High-fat diets result in increased testosterone levels, which have been linked to hair loss—so steaks are not among the foods that prevent hair loss. Stick to leaner proteins such as fish (which has myriad health benefits beyond just maintaining your hair), chicken, soy products, low-fat cheese, eggs, almonds, beans, and yogurt.

6. Water

Proper hydration is a key factor for healthy hair and good health. Every cell and every system in your body uses water to function properly, so don’t just wash your hair in it, drink lots of it. Note that rapid weight loss is another reason for accelerated hair loss. Dropping weight too quickly and/or participating in a fad diet that's not nutritionally sound can cause imbalances in the body and result in increased hair loss.